Dipolar electro-optic structures



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INVENTOR ArraeMa/s United States Patent Office 3,512,876 Patented May 19, 1970 3,512,876 DIPOLAR ELECTRO-OPTIC STRUCTURES Alvin M. Marks, 153-16 10th Ave., Whitestone, N.Y. '11357 Filed June 29, 1964, Ser. No. 378,836 Int. Cl. G021? 1/18, 1/30 US. Cl. 350-267 16 Claims ABSTRACT OF THE DISCLOSURE An electro-optic light controlling device in which a suspension of minute assymetric particles having at least one dimension of the order of A/Zm are subjected to a varying electrical field for the purpose of controlling transmitted or reflected light. Various types of assymetric particles are disclosed.

This invention relates to methods and apparatus for controlling light and related forms of electromagnetic radiation. In particular, this invention relates to novel electro-optical media comprising dipolar particle suspensions and novel methods and apparatus for the electrical or magnetic control of the optical properties of the media by orienting and disorienting the dipolar particles in the suspension.

It has previously been suggested to employ a suspension of orientable dipolar particles as a light-controlling element, and to orient the particles in such a suspension by the application of an external electric or magnetic force field. Devices of this general type that have so far been proposed, however, have had little use because of a number of important deficiencies. One of such prior art faults was the tendency of the oriented particles to coagulate or clump together, rather than remain uniformly dispersed. Another shortcoming was that the optical properties of the devices, either in the oriented or disoriented condition, were of a low order. Thus, when such a suspension Was switched from maximum transmittance to minimum transmittance, or maximum reflectance to minimum reflectance, the obtainable ratios of these transmittances, or reflectances, were too small. Moreover, clear suspensions of dipolar particles, free from light scatter, were not available. Furthermore, the response of such a system to an applied electric or magnetic force field tended to be slow. Orientation and disorientation control techniques were lacking. Consequently, prior art devices were not suitable for incorporation into most electro-optical systems. In general the underlying physical laws gverning electrodichroic systems were not well understood, and the physical parameters of such systems were relatively unknown.

DEFINITIONS Electrodichroic systems as used herein means, dipolar suspensions which exhibit changes in optical properties upon the application of electric or magnetic fields.

Optical density is defined as the negative logarithm to the base of the light transmittance of an optical element. Thus, if the element is completely transparent, it transmits 100% of the incident light, the transmittance is 1.00, and the optical density is -log 1.0, or 0.

Similarly, if the element transmits 10% of the incident light, the transmittance is 0.10 and the optical density is:

Similarly, if an element transmits 1% of the incident light, the transmittance is 0.01, and the optical density is 2. In the same way an element that transmits 0.1% of the incident light corresponds to a transmittance of 0.001, and an optical density of 3, etc.

The electrodichroic ratio is defined as the ratio of the optical density in the opaque condition for dipoles in random orientation, to the optical density in the transparent condition for dipoles partially or completely oriented in the electric field direction.

The parallel electrodichroic ratio refers to the electric field applied parallel to the light path, and the normal electrodichroic ratio refers to the electric field applied normal to the light path.

For most eflYective performance, an electro-optical shutter should be characterized by an electrodichroic ratio of preferably 10 or more.

An electrodichroic ratio of 15, therefore, signifies that the optical density of the shutter in the opaque condition is 15 times that of optical density of the same shutter in the transparent condition.

As a specific example, a shutter capable of transmitting 60% of the incident light in the transparent state, and only 0.1% of the incident light when in the opaque state, would have the following optical densities:

Transparent:

D =log (/60) =0.22 Opaque:

=log 100/ 0.1):3

The electrodichroic ratio of such a shutter, then would be:

The electrodichroic response is defined as the rate of change of electrodichroic ratio with respect to the change in the electric field intensity.

The electrodichroic sensitivity is defined as the rate of change of electrodichroic ratio with respect to the change in electric field intensity, per unit of mass in a unit area in the optical path. Thus the electrodichroic sensitivity is the electrodichroic response per unit mass of a dipole suspension.

Relaxation means the disorientation in the absence of aligning field of previously aligned dipolar particles.

To simplify description of various embodiments of the invention and the methods of making and using the same, it is sometimes useful to employ the following convention: The plane of the cell (which in most embodiments is a thin, fiat container) is taken as the XY plane, X generally being considered the horizontal and Y the vertical aXis. The direction of incident light normal to the plane of the cell is taken as the Z axis. The X, Y and Z axes are all mutually perpendicular.

An object of the present invention, is to provide improved dipole particle suspensions, and methods and apparatus for electrically controlling light and other electromagnetic radiation.

Another object is to provide light-controlling compositions Whose optical properties can be varied electrically without the use of mechanical moving parts.

Still another object is to provide light-controlling compositions and devices as aforesaid, characterized by, improved electro-optical characteristics, greater electrodichroic ratios, greater electrodichroic sensitivity and requiring less time to randomize an oriented suspension in the absence of an electric field.

A further object is to provide an electro-optical sheet having an electrodichroic ratio in excess of 10.

Another object still is to provide a light controlling sheet having electrical means for elfecting dipole relaxation.

Another object is to provide a light controlling sheet having electrical means for effecting dipole orientation or relaxation, which is selectively confined to a particular area.

Yet another object is to provide a thin electro-optical light control device of large area also herein termed a panel or shutter, suitable for use as an electrically controlled variable density window, visor, optical elements, or ophthalmic lens.

A feature of the present invention is the use as a lightcontrolling medium of a suspension of dipole particles having optimum optical and electrical properties resulting from novel relationships established amongst the physical dimensions, resistivity, concentration, and suspending fluid viscosity.

Still another feature is the utilization of the antenna effect influencing the optical properties of dipolar particles, as hereinafter more fully described.

Another feature of the present invention is the control of alignment rise time to maximum transmittance of a suspension of dipolar particles by correlation of concen tration of the dipolar particles, and the viscosity of the suspending fluid, and the application of pulsed electric fields of high intensity.

Another feature is the use of an electric or magnetic field to orient or disorient the dipole particles in such a suspension.

Another feature is the use of current-carrying shielding means for confining a reorienting electric field.

Still another feature is the use of transparent conductive films which serve as electrode means of current-carrying shielding means for establishing different orientations of the dipolar particles to change the transmittance or reflectance of the device.

Another feature of the invention is the use of the curtain effect, and non-current carrying transparent shielding electrodes to reorient a dipolar suspension.

A further feature of this invention is a novel electrooptical iris or curtain diaphragm without mechanical moving parts.

Other objects, advantages, and novel features of the present invention will become apparent from the following more complete description and claims.

In one form, the present invention contemplates a lightcontrolling device employing a suspension of particles hereinafter referred to as dipoles or dipole particles, said particles having at least one dimension large relative to at least one other dimension. The suspended particles are orientable in response to an applied electric, magnetic or mechanical shear field. The application of a nonconstant force field to said suspension enables maximum alignment to be attained without coagulation of the particles.

In another form, this invention contemplates an electrooptical light control device having a cell containing a suspension of dipole particles in a transparent medium, capable of interacting with electromagnetic radiation, said cell having spaced transparent walls and being provided with spaced, transparent electrically conductive films generally parallel with the transparent walls. This embodiment also has a pair of electrodes at oppoosite edges of the cell, near the edges of the transparent walls, and insulated from the conductive films. Such a cell is made transparent by orienting the dipole particles in the suspension with their long dimensions normal to the transparent walls. Orientation is achieved by imposing an electrical potential between the transparent conductive films. The cell is rendered opaque by starting to orient the long dimensions of the dipole particles parallel with the transparent walls, but stopping the orienting influence by imposing an electrical potential of given direction between the electrodes at the edges of the cell, while the particles are in an intermediate, random phase.

In this phase of operation, the field between the two edge electrodes is confined within the cell by simultaneously passing an electric current through each of the conductive films. Passage of such a current effectively prevents the lines of force from short-circuiting through the conductive films and thus by-pass'lng the interior of the cell where the dipole particles are located.

In still another form, this invention contemplates an electro-optical light control device comprising in combination a first cell and a second cell, each of which is enclosed in part by generally parallel, spaced, transparent walls, both of said cells being located in the space between a pair of generally parallel spaced conductive loops. The first cell has a first pair of electrodes located at opposite edges of the cell, and a second pair of electrodes, angularly spaced from the first pair of electrodes by approximately degrees measured in a plane parallel with the transparent walls. The shutter is rendered transparent by imposing an electrical potential between the conductive loops, thus creating an electrostatic field which tends to orient the particles in both cells normal to the transparent walls. When it is desired to render the cell opaque, the loops are de-energized and each of the two pairs of electrodes is connected to a source of electrical potential, thereby creating an electrical field between the first pair of electrodes in the first cell, and a second electrical field between the second pair of electrodes in the second cell. The effect of the two force fields is to orient the dipole particles in the first cell in a first direction parallel to the transparent walls, and the dipoles in the second cell in a second direction parallel to the transparent walls and perpendicular to the direction of the dipoles in the first cell. Since the dipole particles, when aligned normal to the light path, act like polarizing elements, the cross-orientation effectively blocks all but a very small proportion of the light.

The invention consists in the construction, combination and arrangement of parts and of operating steps as hereinafter more fully described and claimed, and as illustrated in the drawings, in which like parts appearing in more than one view are given the same reference numeral throughout, and in which:

FIG. 1 is a fragmentary view on an enlarged scale of an electrically responsive light-controlling structure made in accordance with the present invention showing disoriented dipole particles in a reflecting or light absorbing state.

FIG. 2 is a view similar to FIG. 1, showing the dipole particles in aligned orientation, with the long dimension of the particle normal to the plane of the structure, in a transmittive state.

FIG. 3 is a fragmentary view similar to FIGS. 1 and 2, showing a protective coating between the conductive coating and the dipole suspension.

FIG. 4 is a cross-sectional view showing a structure similar to that shown in FIGS. 1 and 2, provided with an electromagnet to effect orientation.

FIG. 5 is a perspective view of another embodiment of the invention, showing a comparatively bulky high voltage switching device utilizing a single plane dipolar suspension and unshielded electrostatic fields for controlling the orientation of a dipolar particle suspension.

FIG. 6 is a fragmentary diagrammatic detail of a portion of the embodiment of FIG. 5, on a larger scale.

FIG. 7 is a view similar to FIG. 6, showing another stage in the operation of the device in FIG. 5.

FIG. 8 is a schematic diagram of an electrical circuit used to apply potential to the electrodes of the device in FIG 5 FIG. 9 is a fragmentary view, on a greatly enlarged scale, of a single dipole in an elementary volume of suspending fluid.

FIG. 10 is a fragmentary perspective view, similar to FIG. 1, of another embodiment of the invention, namely a refiective-absorptive panel.

FIG. 11 is a partially cut away perspective view, partially schematic, of another embodiment of the invention, in the nature of an electro-optical iris diaphragm.

FIG. 12 is a perspective View of the same electro-optic 

